There has been a wealth of recent interest in the development of adhesive materials that function in wet or underwater environments. In particular, much of this focus has been placed on adhesive development for biomedical applications, as a suitable biomedical adhesive could have an immense impact on health and the economy. Each year, over 230 million major surgeries are performed worldwide, and over 12 million traumatic wounds are treated in the U.S. alone. Approximately 60% of these wounds are closed using mechanical methods such as sutures and staples. Sutures and staples have several disadvantages relative to adhesives, including patient discomfort, higher risk of infection, and the inherent damage to surrounding healthy tissue.
Current FDA-approved adhesives and sealants face several challenges. First, numerous adhesives exhibit toxic characteristics. For example, cyanoacrylate-based adhesives like Dermabond® and SurgiSeal® can only be applied topically due to carcinogenic degradation products. Fibrin sealants like Tisseel and Artiss are derived from blood sources and therefore carry the potential for blood-borne pathogen transmission. Poly(ethylene glycol) (PEG) adhesives are approved as a suture sealants but, due to intense swelling when wet, have the potential to cause moderate inflammatory responses. TissuGlu®, a following subcutaneous implantation, and, in clinical trials, seroma formation occurred in 22% of patients. More important, however, is that most of these adhesives do not possess strong adhesion in an excessively wet environment and are not approved for application in wound closure. In fact, many of these materials specifically advise to dry the application area as much as possible.
In approaching the challenge of developing a strong adhesive for wet applications, many researchers have been inspired by natural glues. Specifically, underwater application and bonding has been demonstrated with materials based on organisms such as sandcastle worms and mussels. Both of these organisms produce proteins containing the non-canonical amino acid 3,4-dihydroxyphenylalanine (DOPA), which has been shown to provide adhesion strength, even in wet environments. In the case of a mussel-mimetic polymer, underwater application was achieved by dissolving the polymer in a chloroform/methanol solution to maintain phase separation from the aqueous environment. The use of toxic organic solvents, however, is not appropriate for biomedical applications.
An alternative method for underwater application uses the phenomenon of coacervation, a form of aqueous liquid-liquid phase separation that is implicated in the adhesion mechanism of sandcastle worms, caddisfly larvae, and mussels. Adhesive coacervate materials mimicking both mussels and sandcastle worms have been developed. To form these coacervates, multiple components needed to be mixed in specific conditions and thus limited their overall applicability. As can be seen, there is a need for a strong adhesive that functions in a wet environment. It would also be desirable if this adhesive could be manipulated in forming a strong seal in the desired environment. It would be further desirable if the adhesive was also non-toxic and may be used in biomedical applications.